1. Field of the Invention
The present invention relates to an improvement in constitution of pressure-connector terminal of a semiconductor device connected to a terminal electrode of a substrate and in a method for connecting thereof.
With continuous effort made for realizing higher level of integration and packing density of LSI in these years, the number of pressure-connector terminals of a semiconductor device increases, while the size thereof decreases. Therefore, it is required for the semiconductor device that individual pressure-connector terminal ensures reliable contact with a corresponding opposite terminal electrode and all pressure-connector temrinals are reliably connected with the opposite terminal electrodes. Moreover, it is also required that a contact resistance value is constant for the all pressure-connector terminals. As explained above, high level reliability is always required recently for connection between pressure-connector terminals and terminal electrodes.
2. Description of the Related Art
Conventional terminal structure and connecting method thereof will then be explained hereunder, taking an example of connection between a pressure-connector terminal and an opposite terminal electrode in a liquid crystal display apparatus into consideration.
FIG. 1 is a plan view illustrating a configuration of a display unit of a liquid crystal display apparatus. In this figure, a liquid crystal display panel 1 and printed wiring substrates 2 are connected with an IC chip 5 (not illustrated) mounted on an insulating film 3. The printed wiring substrates 2 are mutually connected with jumper cables 4.
FIG. 2 illustrates a configuration of IC chip 5 and pattern leads 6, 7 mounted on the insulating film 3. The pattern lead 6 connects terminal electrodes (not illustrated) formed on the liquid crystal display panel 1 and the IC chip 5 and the pattern lead 7 connects pattern leads (not illustrated) formed on the printed wiring substrate 2 and the IC chip 5.
FIG. 3 is a diagram prepared for convenience of explaining the conventional connecting method called a TAB (Tape Automated Bonding) for connecting terminal electrodes and pattern leads. In this figure, a terminal electrode 11 formed on a glass substrate 1a of the liquid crystal display panel 1 is electrically connected with a pressure-connector terminal 6a provided at the end of a pattern lead 6 provided opposed to such terminal electrode 11 via conductive particles 10 included in a bonding material 9. Such bonding material film is called ACF (Anisotropic Conductive Film). Since the pattern leads 6, 7 are formed by etching copper foil bonded with a bonding material 8 on the insulating film 3, the sectional area of the pattern leads is shaped as a trapezoid, owing to the side etching effect. The bonding material 9 is formed of a thermosetting resin or photosetting resin and maintains connection between the terminal electrode 11 and pressure-connector terminal 6a with a contraction stress generated when the bonding material 9 filling the area between the glass substrate 1a and insulation film 3 is hardened.
A pattern lead 6 is generally formed on the insulation film 3 with a pitch of 50 .mu.m and the bottom side of a trapezoid has a length of 25 .mu.m, while the upper bottom, namely width of pressure-connector terminal 6a has the length of 5 to 10 .mu.m. In the case where the contact areas between the surfaces of pressure-connector terminal 6a and terminal electrode 11 are selected, for example, to about 20 points in the electrical contact of the terminal electrode 11 and pressure-connector terminal 6a, it is necessary to provide conductive particles 10. Meanwhile, a grain size of conductive particle 10 is set to 5 .mu.m or larger, only one conductive particle 10 can exist at most in the width direction of the pressure-connector terminal 6a. When the pressure-connector terminal 6a is placed in contact with the terminal electrode 11, the conductive particles 10 of the bonding material 9 at the region where the respective contact surfaces of the pressure-connector terminal 6a and the terminal electrode 11 are provided opposed with each other flow toward the external side of the pressure-connector terminal 6a. Therefore, the conductive particles 10 flow out of such region before the bonding material 9 is hardened, or the conductive particles 10 do not flow out perfectly as shown in the center of FIG. 3 and remain in this region in unstable condition. Generally, 20 or more conductive particles 10 must be provided at the connecting area of the pressure-connector terminal 6a and terminal electrode 11. In the connecting area of the pressure-connector terminal 6a and terminal electrode 11 where connection of conductive particles 10 are insufficient, a connecting resistance between the liquid crystal display panel 1 and IC chip 5 becomes large. Moreover, if resistance values of respective connecting areas are varied, reliability of terminal connection is remarkably lowered.
On the other hand, a terminal connecting method using a bonding material not including conductive particles has also been used for the mounting of semiconductor chips. FIG. 4 is a diagram prepared for explaining a conventional connecting method for connecting the terminal electrodes on the substrate and bumps for IC chips. In this figure, a plurality of bumps (pressure-connector terminals) 13 in such a size of about 50 .mu.m.times.50 .mu.m are formed on the lower surface (face) of the semiconductor chip 12, while the terminal electrodes 15 connected to the corresponding bumps 13 are also formed on the glass substrate 14. In order to obtain good electrical connections, a flatness error of respective contact surfaces of a plurality of bumps 13 and terminal electrodes 15 is designed to 2 .mu.m or lower. After establishing the contact between bumps 13 and terminal electrodes 15, a gap between the semiconductor chip 12 and glass substrate 12 is filled with a thermosetting or photosetting resin bonding material 16. Electrical connection between the bumps 13 and terminal electrodes 15 is maintained with a contraction stress of the hardened boding material 16. However, when a size of semiconductor chip 12 becomes larger and an area of a bump exceeds 50 .mu.m.times.50 .mu.m (in the case of connection between the liquid crystal display panel 1 and IC chip 5, explained above), it is extremely difficult to control a flatness error of the contact surface of bump 13 to 2 .mu.m or lower. In addition, contactness between the bumps 13 and terminal electrodes 15 is actually realized in several areas on the contact surface and it is far from possibility for all terminals to have a small contact resistance value.
In the case of the bump 13 and terminal electrodes 15 shown in FIG. 4, a small quantity of bonding material 16 still remains in the area between the bump 13 and terminal electrode 15, it is then hardened to become an insulating film resulting in an event that an electrical contact resistance between the bump 13 and terminal electrode 15 increases.
As a method of overcoming this problem, the Japanese Patent Laid-Open No. HEI 3-142942 discloses a method for forming a stylus or lump type metal protrusion on the surface of pressure-connector terminal with the electrodeposition method. However, in this method, since a metal protrusion is formed by the electrodeposition method, the metal protrusion is peeled, easily generating electrical short-circuit between pressure-connector terminals. Therefore, it is restricted to make smaller the pitch of the pressure-connector terminals.
From the viewpoint of the mounting of device, it is desirable that good or no-good connecting condition of a large amount of pressure-connector terminals can be discriminated in the course of mounting. However, it has been impossible in the conventional method to inspect the connecting condition until the mounting is completed, even if a defective point has been found.
Meanwhile, the Japanese Patent Laid-Open No. SHO 62-132331 discloses a method for solving this problem. FIG. 5 is a diagram prepared for explaining the method of the above reference for preventing diffusion of a bonding material into the connecting area of the terminal electrode and bump for IC chip on the substrate.
As shown in FIG. 5(a), a small amount of first resin 3 is provided at a place on a wiring substrate 1, where is almost the center of an IC chip 4 fixed later. The quantity of first resin is restricted, as shown in FIG. 5(b), to such a degree that the first resin 3 extends but does not reach the pad 5 and the wiring 2' when the pad 5 of IC chip 4 is aligned on the wiring 2' on the wiring substrate 1 and the IC chip 4 is pressed to the wiring board 1 with a pressure application tool 6. Therefore, the first resin 3 never enter the area located between the pad 5 and wiring 2'. Next, after the first resin 3 is hardened, the pressure being applied by the pressure application tool 6 is released and thereby electrical connection between the pad 5 and wiring 2' can be maintained. Thereafter, as shown in FIG. 5(c), the area between the IC chip 4 and wiring substrate 1 is filled with a second resin 7 for ensuring the more rigid bonding.
However, in the method disclosed in FIG. 5, nonuniform stress is generated in the IC chip 2, since the hardend first resin 3 is located at the central portion of the IC chip 4. This causes easily degradation of the contact resistance.